Stable Numerics Subroutine Library
Programming Reference Manual
Version 1.1 DD-00006-011

3.1.1 Singleton Interval

The map for a real number r∈R  in interval space, X-→ IR  would hence correspond to

X ={r∈R :x=x =r}= [r,r]

This is called a singleton interval, where   -
r=r . The reverse map on a singleton interval is defined as being       -
r= x= x . For non-singleton intervals the map IR-→ R  is generally defined as the midpoint between the interval limits, however multiple further definitions exist - see the chapter on Interval Intrinsic Functions for a listing on the supported methods.